Navien NP Condensing Tankless Gas Water Heater - Service Manual

7.3. Flushing the Heat Exchanger
For proper operation, unit longevity and warranty adherence, water supply to the water heater
meet National Secondary Drinking Water Regulations. In areas with hard water, a water softener
or other conditioning may be needed. A periodic flushing procedure may also be required.
Below is the proper flushing procedure:
1. Disconnect electrical power to the water heater.
2. Close the shut off valves (V3 and V4) on both the hot and cold water lines
3. Connect the pump outlet hose (H1) to the cold water line at the service valve (V2).
4. Connect the drain hose (H3) to service valve (V1).
5. Pour approximately 4 gallons of virgin, food grade, white vinegar or critic acid pail.
6. Place the drain hose (H3) and the hose (H2) to the pump inlet into the cleaning solution.
7. Open both service valves s(V1 and V2) on the hot and cold water line.
8. Operate the pump and allow the cleaning solution to circulate through the water heater for least 4 minutes.
9. Turn off the pump.
Hot Water Line
Cold Water Line
10. Rinse the cleaning solution from the water heater by:
a. Remove the drain hose from the bucket
b. Close service valve (V2) and open shutoff valve (V4).
Do not open shutoff valve (V3).
c. Allow water to flow through the water heater for 5 minutes.
d. Close service valve (V1) and open shutoff valve (V3).
11. Disconnect all hoses.
12. Remove the inline filter at the cold water inlet and clean out any residue.
13. Place the filter back into the unit.
14. Restore electrical power to the water heater.
©Navien America Inc. 2010
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NR/NP series service Manual
Version 2.0